Dyeing of cellulosic material with vat dyestuffs



ijnited rates FatentQhice 3,9775% Patented Feb. 12, 1963 3,677,37d BYEIWG 6F CELLULQSKC MATERIAL WITH VAT DYESTUFFS Wiliiam EZiiby and Cedric Hitchcn, Lancaster, Engiand,

asslgnors to dtandi'ast Dyers dz Printers Limited, Lancaster, England, a British company No Drawing. i iied Mar. 26, 1959, der. No. iildidd Ciairns priority, application Great Britain Apr. 8, 1953 Claims. (1. 8--3 This invention relates to a process for dyeing cellulosic material with vat dyestufis.

A previously proposed process for the continuous dyeing of cellulosic materials with vat dyestufis comprises impregnating the material with a fine aqueous suspension of the dyestufi, removing the surplus liquor by passing the material through a padding mangle, treating the material with an all aline reducing solution (usually an aqueous solution of caustic soda and sodium hydrosulphite), and passing the material through a bath of molten metal. The soluble alkaline leuco-compound of the vat dyestutf, formed by the alkaline reducing solution, has an afinity for the cellulosic mateiral, and the dyestufi is therefore fixed in the material. However, due to the speed of this continuous process, full reduction and fixation of the dyestufi' is not always obtained. Also, any attempt to ensure full reduction and fixation by applying to the material in some degree at the padding stage an alkaline solution of leuco compounds instead of an aqueous suspension of dyestui'i, results in tailing difliculties due to the afiinity of the leuco compounds for the cellulosic material.

It has also previously been proposed to dye ce'llulosic material with vat dyestufi' by impregnating the material with a suspension of acid leuco vat dyestufi prepared by reducing the vat dyestuff with thiourea dioxide at an elevated temperature under neutral or acid conditions, allowing such acid leuco vat dyestuff to oxidize to vat dyestuir' in finely divided form within the cellulosic material, and thereafter subjecting the material to alkaline reduction to fix the vat dyestufi upon the fibre. In this case, the acid leuco vat dyestufi has little afiinity for cellulosic material and tailing is therefore avoided. However, the process is slowed somewhat by the step of oxidizing the acid leuco vat dyestufi, and moreover the process involves transfer of the material to a jigger in which the alkaline reduction step is effected.

An object of the invention is to provide a speedy, economical and continuous vat dyeing process in which tailing difiiculties are avoided.

According to the invention a process of dyeing cellulosic material with vat dyestufr comprises impregnating the material with a suspension of acid leuco vat dyestufi and while the dyestufi in the material is in the acid leuco form treating the material with an alkaline liquor so as to convert the dyestuii in the material to the alkaline leuco form.

Thus, the alkaline leuco compound of the dyestufi is formed directly within the material, the steps of the oxidation of the acid leuco compound and treatment with the usual reducing chemicals being avoided. Also, there are no tailing difiiculties at the padding mangle.

Preferably the material with alkaline leuco dyestufi therein is passed through a heater to complete the fixation of the dyestufi.

Preferably also the heater consists of a molten metal continuous dyeing machine. In this connection, it is found that suspensions of the acid leuco-compounds of vat dyestuffs, when prepared by the neutralisation with acid, in the presence of a suitable dispersing agent, of the alkaline leuco-compounds, contain decomposition prodnets of the sodium hydrosulphite used for reduction.

Such decomposition products, particularly the sulphides formed, attack the molten metal of the continuous dyeing machine, causing formation of a sulphide scum and excessive loss of metal.

This disadvantage is avoided according to a further feature of the invention by use of a suspension of acid leuco vat dyestuff produced by treating the vat dyestufl with thiourea dioxide at elevated temperature and under neutral or acid conditions.

Preferably also the alkaline treating liquor floats on the surface of the molten metal at the entry to the molten metal.

The alkaline treating liquor may be an aqueous solution of caustic soda, or of caustic soda containing sodium hydrosulphite.

Materials dyed by the process according to the invention are or" good appearance, well-penetrated and in the case of most dyestuffs, fuller in shade than comparable dyeings produced by the application of the vet dyestuffs themselves at the padding stage.

The following examples are given, but merely to illustrate the invention:

Example 1 A liquor containing the following quantities of vat dyestuif and chemicals was heated to 9095 C. for five minutes with constant stirring:

A fine suspension of the acid leuco-compound of Caledon Golden Orange 3G was produced.

This suspension of the acid leuco-compound of the dyestufi was cooled to C. and cotton cloth was impregnated evenly with the suspension on a padding mangle, in such a way that the material retained about of its own weight of padding liquor. Directly after impregnation, the material was passed through a molten metal continuous dyeing machine as described in our British patent specification No. 620,584. The molten metal was maintained at a temperature of 95 C. and the floating bath at the entry to the molten metal contained an aqueous solution of caustic soda, 4O gms./litre, and sodium hydrosulphiteS gms./litre, at C, The dyeing was then completed in the ordinary way by oxidation, soaping and rinsing.

The orange dyeing produced was of excellent appearance, penetration and levelness.

Example 2 A liquor containing the following amounts of vat dyestuff and chemicals was heated to the boil for 5 minutes and then allowed to cool to 60 C.:

Guts/litre Caledon Blue XRC single paste (Colour Index Vat Cotton fabric was impregnated evenly, at the padding mangle, with the suspension of the acid leuco-compound of Caledon Blue XRC thus obtained, the padded ma- Guts/litre RD. Caledon Brilliant Orange 6R powder fine (Colour index Vat Orange 3) 30 "Disper'sol AC Caledon Salt A l Diso'clium hydrogen orthophosphate 5 Thiourea dioxide 50 Thesuspension of the acid leuco-compound of the dyestutf so formed was cooled to 60 C. and applied .evenlyto cotton fabric by padding, the material retaining approximately 70% of its own weight of the padding liquor. v

Directly after padding, the material was continuously passed through the molten metal dyeing machine of Example l, theqmolten metal being maintained at 95 C.

The entry bath of the machine contained an aqueous solution of caustic soda of 40 guns/litre at 90 C., and the dyeing was completed in the normal manner by oxidation, soaping and washing.

The resultant dyeing was of excellent appearance, pene- "tration andlevelness'and deeper in shade than a comparabledyei'ng produced by the normal process in which a suspension of, the unreduc'ed vat dyestuif was applied -at the padding stage.

Example 4 A liquor. containing the following amounts of chemicals and vat dyestuffs Was heated to 90-95 C. for '5 minutes with constant stirring:

g Guts/litre Caledon l 3rown R single paste (Colour Index.Vat

Browne) the dyestutiohtained by treating. 4:5- dibeuzoylaminod:1'-dianthrimide with sulphuric ac d, c.f Thorpes Dictionary of Applied Chemistry, fourth edition, vol. 1,, p, 422 Caledon Brown G single paste (Colour Index Vat -Bro wn 3 mixed with Colour Index Vat Black 27) (a mixture of the dyestuffobtained by treating 4 1 4- dibenzoylarnino-l :l dianthrimide wit-h sulphuric acid, of. Thorpes Dictionary of Applied Chemistry, fourth edition, vol. I, p. 422, and Cnledon Brown RS above) 1 i i Caledon-Dark Brownj 31; single paste (Colour Index .,Vat Brown 1 Dispersol AC A v I 1 Disodium hydrogen orthophosphate 5 Thlouz'ea dioxide The resultant fine suspension of the acid leuco-compounds'of the dyestuffs was allowed to cool to C. and then applied evenly to linen fabric by a padding process. Directly after padding, the fabric was passed through the molten metal dyeing machine of Example 1, the molten metal being maintained at 95 C. The entry bath of the machine contained an aqueous solution of caustic soda, 40 gms./litre and sodium hydrosulphite '5 gms./litre at -C. Dyeing was completed in the normal way by oxidation, soapin'g and washing. The tan shade produced was of excellent appearance, levelness and penetration.

The invention also comprises cellulosic materials whenever dyed with vat dyestuffs by any of the foregoing processes according to the invention.

Use may also be made of the inventions described in our British patent specifications Nos. 661,086, 663,066, 665,454 and 681,983.

We claim:

1. A process of dyeing cellulose with vat dyestutf, comprising impregnating a continuous length of cellulose with a suspension of a thioure'a dioxide-reduced acid leuco vat dyestuif, treating the impregnated cellulose with an alkaline liquor, While the dyestuff in the material is in the acid leuco forrrn'so as to convert the dyestufi to the alkaline leucoform, and passing the cellulose through the molten'metal'of a'molte'n metal continuous dyeing machine'to complete the fixation of the dyestufi.

2 A process according to claim 1, wherein the molten metal is maintained 'at approximately C.

3. A process according to claim 2, wherein the alkaline treating liquor is a hot aqueous liquor floating on the surface of the molten metal at the entry to the molten metal.

4. A processacc'or'ding to claim 3, wherein the alkaline treating liquor is a hot aqueous solution of caustic soda.

5. A process'according to claim 3, wherein the alkaline treating liquor, is 'a hot aqueous solution of caustic soda and sodium hydrbsulphite.

References Cited in the file at thispatent UNlTED STATES PATENTS 

1. A PROCESS OF DYEING CELLULOSE WITH VAT DYESTUFF, COMPRISING IMPREGNATING A CONTINUOUS LENGTH OF CELLULOSE WITH A SUSPENSION OF A THIOUREA DIOXIDE-REDUCED ACID LEUCO YAT DYESTUFF, TREATING THE IMPREGNATED CELLULOSE WITH AN ALKALINE LIQUOR, WHILE THE DYESTUFF IN THE MATERIAL IS IN THE ACID LEUCO FROM, SO AS TO CONVERT THE DYESTUFF TO THE ALKALINE LEUCO FORM, AND PASSING THE CELLULOSE THROUGH THE MOLTEN METAL OF A MOLTEN METAL CONTINUOUS DYEING MACHINE TO COMPLETE THE FIXATION OF THE DYESTUFF. 